Conventionally, in a system for managing article information, article information is managed using contactless communication using an electromagnetic field between an RFID tag attached to an article and a reader that reads tag information of the RFID tag.
Patent Document 1 (identified below) describes a configuration in which a metal surface of a metal article is used as a radiator of radio waves from an RFID tag in a case where the RFID tag is attached to the metal article, for example.
Referring to FIGS. 16A and 16B, Patent Document 1 describes a magnetic field antenna capacitively coupled to a radiation plate 115 in which a thin metal plate is attached to a base 110. A coupling electrode 135 electrically forms an annular electrode through capacitive coupling between opposing ends 136c, 136d to function as a magnetic field antenna. The coupling electrode 135 includes a pair of coupling parts 136a, 136b coupled to a radio IC chip 105.    Patent Document 1: JP 5510450 B2.
FIG. 17 is an equivalent circuit diagram of a radio IC device shown in FIGS. 16A and 16B. The coupling electrode 135 has an inductance component La, internal capacitance Ca of the radio IC chip 105, capacitance Cb between the opposing ends 136c, 136d, and capacitance Cc between the coupling electrode 135 and the radiation plate 115. An antenna shown in FIGS. 15A and 15B is described as a magnetic field antenna, the resonant circuit constitutes a resonator whose impedance becomes infinite (an actual measured value is in a range of several KΩ to several MΩ depending on the Q value of the inductance element) when impedance measurement is performed across the radio IC chip 105 with the internal capacitance Ca left as stray capacitance.
The coupling electrode 135 having such a circuit configuration functions as a magnetic field antenna and allows the radiation plate 115 to generate radio waves by radiating a magnetic field. As described above, the radio IC device described in Patent Document 1 communicates by causing a metal surface thereof capacitively and magnetically coupled to the metal surface of the article to generate an electric field and radiate radio waves into the air. However, no electric field is generated from the radio IC device itself, a communication distance of the radio IC device itself is as short as several mm to several cm. This makes the communication distance small even when a radio communication device is attached to metal.